Hello, I would like to propose making inits and tails less strict: inits :: [a] -> [[a]] -inits [] = [[]] -inits (x:xs) = [[]] ++ map (x:) (inits xs) +inits xs = [] : case xs of + [] -> [] + x:xs -> map (x:) (inits xs) tails :: [a] -> [[a]] -tails [] = [[]] -tails xxs@(_:xs) = xxs : tails xs +tails xxs = xxs : case xxs of + [] -> [] + _:xs -> tails xs Having a lazier inits allows the elegant: nats = map length (inits nats) which loops for the current definition. This definition was due to John Tromp: http://www.mail-archive.com/haskell@haskell.org/msg21044.html Discussion deadline: 2 weeks. Regards, Bas